Telegraphic transmission by space discharge control



May 5, 19,42. 7 POTTS 2,281,596

TELEGRAPHIC TRANSMISSION BY SPACE DISCHARGE CONTROL Filed March 7, 19382 Sheets-Sheet 1 INVENTOR LOUIS M. POTTS ATTORNEY FIG.1

May 5, 1942. 1.. M. POTTS 2,281,596

TELEGRAPHIC TRANSMISSION BY SPACE DISCHARGE CONTROL Fiied March 7, 19382 Sheets-Sheet 2 250 237 350 239 354 Z aka-4- 243 1(" /25| 277 L up 263l l INVENTOR LOUIS M POTTS ATTORNEY Patented May 5, 1942 TELEGRAPHICTRANSMISSION BY SPACE DISCHARGE CONTROL Louis M. Potts, Evanston, Ill.,assignor to Teletype Corporation, Chicago, 111., a corporation ofDelaware Application March 7, 1938, Serial No. 194,305

12 Claims.

This invention pertains to telegraph systems and apparatus and moreparticularly to such systems in which distance between terminal stationsrenders necessary an intermediate station equipped with repeatingdevices to renew the strength of the signal impulses.

The invention pertains more particularly to systems which serve a largetraffic at a high speed of transmission in which time required foroperation of mechanical armatures of magnetic relays may become arestraining feature in the speed of operation of the system both fromthe viewpoint of speed of generation of telegraphic impulses and alsofrom the viewpoint of repeating the impulses at a repeater station wheretransit time of an armature in an electromagnetic relay introducesdistortion into the time dimension of a repeated impulse.

The main object of the present invention resides in the provision oftelegraph signal instrumentalities which are capable of satisfactory andreliable operation for high speed transmission and which do notintroduce detrimental distortion at such transmitting speeds.

Accordingly, the present invention has as its principal features theprovision of terminal transmitting equipment in which telegraph signalimpulses are generated by thermo-electronic and photo-electronic devicesfor transmission, and the provision of terminal receiving equipment inwhich received impulses are amplified by electronic devices forrecording, together with repeating equipment comprising reflectsuppression means and electronic devices wholly independent of anymechanically movable member.

Further objects and features of invention are embodied in details ofelements of the assembled system and in variations of the preferred formof the invention; namely, to provide circuits to efiect two-waysingle-line transmission through a repeating station including means forgeneration of opposing potentials to prevent reflection signals,generating signal impulses in alternating current form and rectifyingthe alternating current signal impulses for transmission as directcurrent signals, repeating signals by means of a photo-cell andrepeating received double-current signals by means of a polarized lampand a pair of responsive photo-cells.

A better understanding of the invention may station operating upon opencircuit principles according to this invention;

Fig. 2 illustrates a modification thereof operating upon closed circuitprinciples;

Fig. 3 illustrates a repeating structure; and

Fig. 4 illustrates a double-current repeating structure.

A general structure of a system according to this invention isillustrated in Fig. 1 wherein a terminal substation I0 is shownconnected by a line section conductor H, through a main station orrepeating station 12, and thence by a further line section conductor 14to a terminal substation 15 associated with station 10 for inrtercommunication.

Operation of the structure illustrated in Fig. 1, when broadlycontemplated, is upon a principle of telegraphy wherein a line conductornot actively in operation for transmission of intelligence signals, isin a signaling condition without any applied electrical potential,wherein two or more stations have receiving instruments permanentlyconnected in parallel paths from the line conductor to ground, andwherein any station may transmit to all stations by applying anelectrical potential to the line, thereby causing currents to flow fromthe line to operate receivers at all stations including the home stationreceiver.

In Fig. 1, two line conductors I 1, 14 are shown, each of which operatesas described above, the two conductors being illustrated in signalingcondition without electrical potential and being permanently associatedas line sections with receiving recorders and with repeating equipmentto communicate to the associated line section any signaling potentialimpressed upon either line section.

Line section I I has two permanently connected receivers; namely, arecorder receiver I61 connected from conductor 11 through conductor 11and amplifier l9, and a repeater receiver connected from conductor ll,through conductor 21, oscillator valve 32, amplifier valve 115, andrepeating coil 183. Line section 14 has two similar permanentlyconnected receivers; namely, a recorder receiver 169 connected fromconductor 14, through conductor 61 and amplifier 69, and a repeaterreceiver connected from conductor 14 through conductor 4'1, oscillatorvalve 52, amplifier valve 24 and repeating coil 2|6. In restingcondition of the system, no potential is impressed upon either linesection conductor, and valves 32, 52 described as oscillator valves arenot in oscillating condition.

{Each station I and I2 on line section II, and I2 and I5 on line section[4, has a transmitter which, when in resting condition, does not producean operating potential upon either line II or I4 but which, whencontrolled to become active by change in illumination condition of aphoto-cell, produces an electrical signaling potential upon itsassociated line section conductor, the transmission circuit thenextending from ground connection at the transmitter, through aunidirectional valve and induction coil winding of the activetransmitter, to the line section conductors, and from the line sectionconductor extending in parallel through the two receivers of that linesection to ground, thus controlling the two receivers; namely, the homerecorder and the repeater receiver, each to manifest a signal of currentnature.

Each such transmitter assembly includes gas filled valve subjected tosufficient potential difference between filament and plate to effectconductivity, the valve being rendered oscillating in operation by acondenser having its terminals connected to filament and plate,respectively. Suchvalve systems in the drawings include gasfilled valvesI9, 32, 52, 69, I38, I40, in Fig. 1, and 231, 295, 296, 320, 340, 348 inFig. 2. These valves are three-electrode gas-filled valves andpreferably may be operated with indirectly heated. cathodes asillustrated in valves 295 and 296, Fig. 2. A condenser, when connectedbetween anode and cathode, causes the valve to act as a relaxationoscillator. It is not necessary in all cases nor with all valves thatthe grid shall actually be positive with respect to the cathode.

Some tubes under certain conditions as, for example, ample platevoltage, oscillate even when the gridv is slightly negative. There issome critical value of potential of the grid which may be slightlynegative or positive at or above which the tube will oscillate, and whenthe potential of the grid is below this value, the valve will not startinto oscillation. When the proper adjustments are made, substantiallydirect current will flow through a conductive resistor-path having itsterminals directly or indirectly connected to the. two terminals of thecondenser, for example, Fig. 1, through path I53, I54, I55, I56, I50,connected toterminals of condenser I51 and valve I9, or path I63, I64,I60 connected to terminals of condenser I65 and valve 32, while valve I9or 32 is in oscillating operation and while an alternating current flowsin condenser I51 or I65. In the drawings, the gas-filled valves areindicated symbolically by gray-code hatching.

It is contemplated in the structures herein shown that oscillations ofthe gas-filled valves will be at a frequency much higher than thetelegraph code-signaling frequency, as, for example, an oscillatingfrequency of 10 kilocycles and a signaling speed of 66 bands.

At station I0, the transmitter system includes photo-cell I05, amplifiervalve I25, oscillator valve I33, induction coil 23 and unidirectionalvalve 4|, connected to line conductor I I. At station I5, thetransmitter includes photo-cell 221, amplifier valve 28, oscillatorvalve I40, induction coil 13 and'unidirectional valve 43, connected toline conductor I4.

At repeating station I2, there are two transmitters, one from ground I90through secondary windings I85, I86 of induction coil I83, throughrectifier valve 60 and inductance 56 to line section conductor I4, andthe other from ground connection 2I3 through secondary windings 2 I4,215,

of induction coil 2I6, rectifier valve 40 and in ductance 36 to linesection conductor II. Re

- peater station I2 contains also echo suppression valves and circuits.

The term oscillating current is used in this specification to indicate acurrent comprising a succession of uniform unidirectional impulsesseparated by time periods of no current or of substantially no current.

The term potentiometer resistor is used in this description to indicatea resistor through which a supply current flows, the resistor beingprovided with adjustable taps or contactors by means of which currentsmay be derived from the potentiometer resistor for operating purposes.

The term potential branch conductor is used in this description toindicate a conductor connected to a current-carrying circuit and connected also to a grid of a valve, current conditions in the circuit beingvariable to vary the potential applied to the grid through the potentialbranch conductor.

Record tapes I04, 226, Fig. l and M8, 3I9, Fig. 2, may be of a standarddesign as illustrated in Patent No. 1,549,907 to Clokey or in copendingapplication Serial No. 48,098 filed November 4, 1935, or of otherdesired design.

Describing the structure of Fig. 1 now with greater attention to detail,line section II is connected in substation I0 through resistor I6 toground connection 2I1, through potential branch conductor I1 to grid I8of receiving valve I9, and line section ll'is connected also throughtransmitting conductor to winding 22 of transmitting inductor coil 23and unidirectional valve 4| to ground connection 42.

In repeating station I2, line conductor II is extended through resistor26 to ground connec tion 2I8, and is connected through potential branchconductor 21 to grid 3I of receiving valve 32, also through conductorand inductance 36 to cathode 39 of retransmitting rectifying valve 40,while line conductor I4 is extended through resistor 46 to ground, andis connected through potential branch conductor 41, to grid 5I ofreceiving valve 52, also through conductor and inductance 56 to cathode59 of retransmitting rectifying valve 60.

In substation I5, line conductor I4 is connected through resistor 66 toground, through potential branch conductor 61 to grid 68 of receivingvalve 69, and through transmitting conductor 10 to winding 12 oftransmitting induction coil 13 and unidirectional valve 43 to groundconnection 44.

Apparatus provided further in substation I0 comprises an illuminant IOIand lens I02 producing a beam I03 controlled by records in a controlform I04 to control a photo-cell I05 which is energized by a batteryI06. Details of such an arrangement applied to a Wheatstonecodetransmission tape are described in Patent No. 1,549,907 granted toClokey, and details of such an arrangement applied to a Baudot-codetransmission tape are described and claimed in a copending applicationSerial No. 48,098 filed November 4, 1935, by L. M. Potts. Photo-cell I05and resistor I01 constitute a potentiometer which, through a potentialbranch conductor I00, determines a potential applied to grid I09 ofamplifier valve I25 which, when photo-cell I05 is dark, substantiallyestops current in the plate circuit of the valve. In response to controlof cell I05 by light, the potential of grid I09 is rendered morepositive with reference to cathode I30, permitting a current in theplate circuit ineluding contactor I34, cathode I30, anode I29, resistorI21, contactor I33 and a part of potentiometer resistor II1 as a sourceof energy, the described circuit being a potentiometer circuit having apotential branch conductor I46 extending to grid I41 of gas-filledoscillator valve I38.

Valve I38 has a plate circuit including contactor I32, cathode I3I,anode I39, resistor HI and a portion of resistor I I1 as a source ofdirect current energy. Adjustment of contactors I32 and I33 is such thatvalve I38 oscillates when photo-cell I is dark and plate current invalve I is minimum. This is the normal resting condition. As shown,contactor I33 is slightly negative with reference to oontactor I32 butmay be slightly positive as permitted or required by characteristics ofthe associated valves and circuits.

When photo-cell I05 is illuminated, grid I09 is made more positive andcurrent flows in the potentiometer plate circuit of valve I25, renderinggrid I41 more negative which stops oscillation of valve I38.

Valve I38 is rendered oscillating in operation by a condenser having itsterminals connected to cathode and anode, respectively. When valve I38oscillates as described, it supplies an alternating current throughcondenser I48 and primary winding I49 of induction coil 23 fortransrmssion purposes, oscillation being stopped in code-signal mannerby a more negative potential applied to grid I41 b control of photo-cellI05 when illuminated. When alternating current flows in primary I49, thesecondary 22 as permitted by unidirectional valve 4I supplies apotential of oscillating current of positive po larity to line sectionconductor II.

In substation I0, a local recording circuit includes a part ofpotentiometer resistor I56, contactor I50, filament I5I of valve I8,plate I52, resistor I53, recorder relay I54, and conductor I55, valve I9being rendered oscillating by condenser I51. Current through recordermagnet I54 is substantially constant direct current.

An armature and back contact on receiving relay I54 energizes arecording selector magnet I61 over an obvious circuit.

In the repeating station I2, :1 previously mentioned potential branchconductor 21 is connected from the line section conductor II forrepeating purposes through resistor 28 and condenser 30 to grid 3I ofgas-filled oscillator valve 32 with a plate circuit including contactorI60, filament I6I, plate I62, resistor I63, and part of potentiometerresistor I64 as a source of direct current energy. Condenser I65 rendersthe valve 32 oscillating. An output circuit for oscillator valve 32includes grounded battery I66, resistor I63, condenser I10, resistor HI,and ground, the described output circuit constituting a potentiometer tosupply a variable potential over conductor I13 to grid I14 of amplifiervalve I15 from which valve the output current is an oscillating currentin a circuit including contactor I18, conductor I11, filament I80, plateI8I, primary winding I82 of induction coil I83, conductor I84, and apart of potentiometer resistor I64 as a source of direct current energy.Oscillating current in winding I82 generates alternating currents inboth halves I85, I86 of a secondary winding which is rectified byrectifying valve 60 and is applied as a direct current to line sectionconductor l4, the retransmitting path including ground connection I90,both halves I85, I 88 alternately of the split secondary winding ofinduction coil I83, alternately over conductors ISI, I82 and plates I83,I 84, thence as direct .or rectified current over filament 58,,conductor 55, inductance 56 to line section conductor I4, the retransmission circuit being completed to ground through resistor 46 in repeatingstation I2 and resistor 66 in substation I5 connected in parallel toground.

Equipment provided at substation I5 duplicates the equipment describedfor substation I0, including a receiving valve 69, potentiometerresistor 20I, contactor 202, plate 206, resistor 201, receiver relay208, condenser 209, and recorder selector magnet I89.

In repeating station I2, a previously mentioned branch potentialconductor 41 is connected from the line section conductor I4 throughresistor 48 and condenser 50 to a grid 5I in a gas-filled receivingoscillator valve 52 analogous to the receiving valve 32. An alternatingcurrent is generated in resistor M2 and grid 2I3, thus generating anoscillating current in winding I81 and alternating currents in windings2I4 and 2I5 of induction coil 2I6, which alternating currentsarerectified by valve and are applied to line section conductor II assignals of current of positive potential with reference to groundconnections 2I1 and 2I8.

Means for estoppel of reflection signals in the repeating station I2 isprovided by induction coil winding 220, rectifier valve HI, andcondenser 50. An initial positive electrification of line sectionconductor II and associated grid 3| results in oscillation of valve 32which produces an oscillating current in primary winding I82 ofinduction coil I83, thereby producing alternating potentials insecondary induction coil winding 220 which, as permitted. by rectifyingvalve 22I, results in charging the condenser over a circuit includingfilament 222, plate 223, Winding 220 as a source of energy, conductor224, condenser 50, and conductor 225, which current maintains condenser50 charged with its negatively charged terminal connected to grid 5I,thus maintaining the grid 5| negative with reference to contactor 2 aslong as conductor 225 remains positively electrified, despite positiveelectrification of line section conductor I4. Resistor 49 provides aleak circuit for discharge of condenser 50 after cessation of thesignal.

Rectifier valves and HI have their plates electrified simultaneously bysecondary windings of induction coil I83, and both of the valves applytheir rectified currents to the grid 5I, positively and negatively,respectively, but precedence is given to valve 22I by direct connectionover conductor 225 from its filament 222 to grid 5I while a delayingelement illustrated in the form of a network comprising an inductance 56and two condensers 51 is included in the connection of valve 60 from itsfilament 59 through conductor 55, inductance 56, local extension of linesection conductor I4, conductor 41, resistor 48, and condenser 50 togrid 5|. Accordingly, the grid 5| is electrified negatively by inductioncoil Winding 220 and valve 22I in advance of reflectional positiveelectrification of conductor I4 by valve 60 and reflection signals areestopped. By virtue of its position in the circuit structure illustratedat I2 in Fig. l, the filter 56, 51 acts to filter out any high frequencyoscillations and also acts as a signal delaying network in the mainretransmission circuit extending from filament 59, over line sectionconductor I4 to substation I5. Any distortion introduced by thi networkis insignificant and does not interfere with the signals.

Operation of the structure illustratedin Fig. 1, when considered inreview, is briefiyas follows: For a resting period, a signal of markingnature is generated throughout the system. Photo-cells I05 and 221 areilluminated, signal-receiving selector magnets I61 and I69 areenergized, and there is no current on line section conductors II and I4which are at ground potential by virtue of connection to ground throughresistors I6, 26, 46, and 66.

Illumination of photo-cell I05 effects conductivity in vacuum valve I25which produces a potential of more positive polarity on grid I09 ofvalve I25 and a potential of more negative polarity on grid I41, thusestopping oscillation in gasfilled valve I38 and thus estoppinggeneration of any potential in secondary induction coil winding 22connected to line section conductor II. An identical condition ismaintained in photo-cell 221, vacuum'valve 28, "gas-filled valves I40and secondary induction coil winding 12 connected to line sectionconductor I4.

In repeating station I2, ground potential upon grids 3| and 5| ofgas-filled valves 32 and 52 estop oscillation, and no potential isgenerated upon conductors 35 and 55 connected to line section conductorsII and I4.

To generate a signal of spacing nature in the system, transmittingmechanism controlled by tape I04 interrupts beam I03 todarken valve I05to vary the potential on grid I09 to render the valve I25non-conductive, thereby permitting grid I41 to acquire the potential ofcontactor I33 to permit. oscillation in the system of gas-filled valveI38, thereby producing potentials in secondary induction coil winding 22to produce a signal current of positive potential on line section II,thus activating valve I9 to operate home recorder relay I54 todeenergize home recorder selector magnet I61 to effect a spacing signal.in its recorder, and activating also valve. 32 which in turn activatesvalves I15 and 60 to produce a signal current of positive potential online section I4 (and a negative signal potential on condenser and ongrid 5| to estop reflection signals), thus activating valve 69 tooperate remote receiver relay 208 to deenergizerecorder selector magnetI69 to effect a spacing signal'in its recorder.

The structure illustrated in Fig. 2, when broadly contemplated, isoperated upon the closedcircuit single-current principle of telegraphywherein a line conductor, when not active in communication, carries acontinuous and uniform electrical, current, in which all stations havereceiving instruments permanently con- .nected in series in the circuitof the line conductor, in which a source of current is included in thecircuit of the line conductor, and in which an operator at any stationmay impress a signal upon the circuit of the line conductor by openingand closing that circuit in code manner to operate receivers at allstations including the home station receiver.

In Fig. 2, two line conductors are shown each of which operates asdescribed above, the two conductors being associated as line sectionsthrough repeating equipment to communicate to the associated linesection any spacing signal impressed upon either line section.

Described briefly, substation 230 is connected over line sectionconductor 23I to repeater station 232, which is connected by a furtherline section conductor 233 to a second substation .23

and each of the two line sections carries a current generated at therepeating station 232. Line section circuit 23I comprises a lineconductor 23I, alocal conductor 21.1, two resistors 262, 218, asubstation receiver 320, a repeating station receiver 263,. a substationkeying valve 261, and a source of current comprising an oscillator valve231 generating an oscillating current, an induc tion coil 256 generatingalternating potentials from the oscillating current, and arectifiervalve 213 generating from the alternating potentials a rectified currentfor signaling. Corresponding equipment is provided for line sectionconductor 233. Repeating station 232 has means for echo suppression.

Described in greater detail, line section circuit 23I extends fromground connection 260 at substation 230 to ground connection 26I atrepeating station232, through resistor 262, filament 265 and plate 266of keying valve 261, line section conductor 23I, filament 210 and plates21I, 12I ofrectifying'valve 213, local conductors 215, 216, inductioncoil windings 351, 358, two induction coil windings 251, 258 as a sourceof alternating potential, for energy, local conductor 211, and resistor218. A similar line section circuit 233 extends from ground connection280 at substation 234 to ground connection 28! at repeating station 232.

Energy for the line section circuit 23I is generated at repeatingstation 232 by a gas-filled oscillator valve 231 having a cathodeconnected to contactor MI and a grid connected to contactor 249. Bothcontactors are on potentiometer resistor 240, the potentials of the gridand cathode being such that valve 231 oscillates by reason of condenser244 and generates an alternating current in primary winding 238 ofinduction coil 239. Alternating potentials are generated in secondarywinding 241 of induction coil 239, effective upon-grid 250 of amplifierValve 25I to generate an oscillating current in prinarywinding 255 ofinduction coil 255. Responsive to oscillating current in primary winding255, alternating potentials are generated in companion secondarywindings 251, 258 which, cooperating with rectifier valve 213, produce arectified current for signaling in the line section circuit 23I.

At substation 230,-energy from the described line section circuit 23I isapplied through resistor 323 and potential branch conductor 322 to grid32I to control an oscillator valve 320 to energize a recorder relay ormagnet 330 in a plate circuit including cathode 321, anode 328, resistor329, recorder magnet 330, potentiometer resistor 33I and contactor 326,the valve 320 being rendered oscillating by condenser 332. Recorder 330may be any type of recorder responsive to direct current such asillustrated in U. S. Patent No. 1,904,164.

At repeating station 232, energy from the line section circuit extensionconductor 211 controls potential upon a gridof a signal receivingvacuurn valve 263, rendering the grid more negative than groundpotential and sufiiciently negative with reference to the cathode ofvalve 263 to render the plate circuit of the valve nonconducting. Thenon-conducting condition of valve 263 permits the grid of a gas-filledoscillator valve 340 to attain the potential of contactor 264 while itscathode manifests the poten tial of contactor 263, the two potentialshaving a difierence such that. oscillator valve 340 is permitted tooscillate, which, through induction coil M amplifier valve .342, n indution coil-343,

supplies signaling current to line section conductor 233. Similarequipment is provided for line section conductor 233 and its extensionconductor 243.

Also at substation 233, the valve 261 operates as a keying device fortransmission over the described line section circuit 231. When photocell293 is illuminated as a marking signal, the potential of the grid ofvacuum valve 291 is rendered such that the plate circuit of valve 291 isrendered conducting, rendering the grid of gas-filled oscillator valve295 more negative, thus stopping oscillation of Valve 235 andterminating all generation of energy in secondary induction coil winding310. Accordingly, grid 313 of valve 261 attains the positive potentialof grounded battery 315, rendering conductive the plate circuit of valve261, thus rendering conductive the entire line circuit section 231, fromground connection 260 to ground connection 261. Corresponding equipmentincluding the keying valve 333 is provided at substation 234 for keyingof line circuit section 233.

Circuit 3533, included in repeating station 232 to provide means againstreflection signals, includes a secondary winding 351 in induction coil256, a secondary winding 352 in induction coil 253, a unidirectionalvalve 354, a condenser 355 and resistor 356 connected to grid ofoscillator valve 231. Induction coil 353 has two primary windings 351,358 included in conductors 216, 215 and in series with secondarywindings 251 and 253, respectively.

While a signal current condition is' being impressed upon line sectionconductor 231, alternate impulses pass through windings 358 and 35-1,respectively, so as to produce an alternating magnetic flux in inductioncoil 353. Secondary windings 351 and 352 are so proportioned that theyproduce substantially opposite and equal potentials, producing nopolarization of condenser 355. However, since the two oscillators 231and 343 are maintaining line signaling currents of positive potentialupon local conductors 243 and 211, polarization of grid of valve 231from conductor 243 and polarization of grid of valve 345 from conductor211 maintains the valves 231 and 348 in oscillation.

When for transmission of telegraph signals of an intelligence code thephoto-cell 280 is darkened, increase of resistance of the photo-cellcauses the grid of vacuum valve 291 to become more negative, currentceases to flow in the plate circuit of vacuum valve 291 and the grid ofgasfilled oscillator valve 235 attains the potential of contactor 233and thus becomes more positive, permitting gas-filled valve 295 tooscillate by reason of condenser 306. There is generated in the primarywinding of induction coil 304 an alternating current and in thesecondary winding 310 an alternating potential and a pulsating currentby reason of unidirectional valve 311. The pulsating current charges acondenser 312 connected in series with battery 315, overcoming thepositive polarity of battery 315 and causing grid 313 to becomesufiiciently negative to render non-conducting the plate circuit of thekeying valve 261, thereby interrupting in keying manner the describedcurrent in line section circuit 231.

Cessation of current in line section circuit 231 has a controllinginfluence upon three units of associated apparatus, permitting the gridof valve 320 to attain ground potential from ground connection 263,permitting the grid of valve 263 to attain ground potential from groundconnection 261, and terminating generation of alternating potentials ininduction coil Winding 352.

Ground potential upon the grid of valve 323 renders the grid morenegative than before, stopping oscillation in valve 323, deenergizingrecorder magnet 333 and producing a spacing signal in the recorder.

Ground potential upon the grid of valve 263 makes the grid more positivethan before, renders the plate circuit of valve 263 conducting, thusmaking the grid of valve 340 more negative and stopping oscillation ofvalve 340, which renders inert induction coil 341, valve 342, inductioncoil 343 and rectifier 341, terminating current in line section 233 andproducing a spacing signal in the line section 233 and in the receivingvalve 343.

Termination of generation of alternating potentials in induction coilwinding 352 leaves unopposed the potentials generated in induction coilwinding 351 which, acting through unidirectional valve 354 will chargecondenser 355 to impress upon the grid of valve 231 a potential whichwill maintain the valve 231 in oscillation despite a reflectioncondition immediately to be manifested upon conductor 243. By cessationof current in line section 233 the grid of vacuum valve 282 is permittedto attain ground potential through ground connection 281, making thegrid more positive than before and rendering the junction point 283 morenegative than before, but the now charged condenser 255 overcome theinfluence of valve 282 and holds the grid of valve 231 suflicientlypositive to maintain the valve 231 in oscillation. Thus echo suppressionis eiiected by an opposition of concurrent potentials, from valve 282and from circuit 253, respectively.

During continuance of the line signal of spacing nature originating insubstation 250, the valve 231 oscillates, valve 340 does not oscillate.Alternating potentials are generated in secondaries 251, 258 ofinduction coil 258, but current does not flow in conductors 211, 231,233, 243.

Upon reillumination of valve 293 to terminate the spacing signal and torestore the line signal of direct current nature, valve 231 becomesconducting, currents fiow in secondaries 251, 253 and in conductors 211,231, the grid 335 becomes biased positively, valve 340 beginsoscillating and current begins in conductor 233.

In review, operation of the structure illustrated in Fig. 2 is brieflyas follows: With photo-cells 2911 and 368 illuminated, plate circuits ofvalves 291 and 292 are conducting, gas-filled valves 235 and 296 arenon-oscillating, induction coils 354 and 3115 are inert, the grids ofkeying valves 313 and 333 are made positive by their biasing batteries315 and 316, rendering the two keying valves conducting, valves 231 and323 are continuously in oscillation and supply rectified current ofpositive potential to line sections 231, 233 and to receiving valves 328and 343 while current of negative potential is supplied to repeatervalves 263 and 282 for a signal of marking nature. Receiving valves 320and 348 in response to positive potential, oscillate and energize therecorders 333 and 349. Negative potential from conductor 211 and 243upon grids of valves 253 and 282 render the plate circuitsnon-conducting and permit gasfilled valves 231 and 340 to oscillate.

To produce a signal of spacing nature, control tape 318 darkens thephoto-cell 290 which renders valve 291 non-conducting and causes cell295 to oscillate, energizing the repeating coil 334 and producing anegative electrification of grid 313 to render keying valve 261non-conducting to interrupt current in line section 23! and to reduce toearth potential the'grid 32! which stops current in recorder 330.Cessation of current in conductors 23! and 211 and leakage throughresistor 21%] reduces the grid of valve 263 to earth potential, thusstopping oscillation of valve 340 and stopping current in line section233, permitting the grid of receiving valve 348 to be reduced to earthpotential, thereby stopping oscillation of. valve 348 and stoppingcurrent in recorder 349, producing therein a signal of spacing nature.

Reflection signals are generated in valve 282 from extension conductor243 but are stopped at the point 283 by counter electromotive force incondenser 355 generated in a local circuit 353 by valve 231 actingthrough induction coil 239, valve 25!, induction coil 256 and valve 354.

The function of relay 269 is to start the system into oscillation,initially. Should batteries be removed to facilitate testor replacementof parts as is customary practice, then upon restoring the batteryconnections, an earth potential upon grids of valves 263 and 282 willrender those valves conducting and would render both valves 231 and 340non-oscillating but for the fact that relay 269 then unenergized willhold open the plate circuit of valve 263, thus permitting the grid ofgas filled valve 340 to attain a potential which will permit valve 340to start into oscillation whereupon the plate current of valve 340willenergize relay 269 over an obvious circuit and also will generate acurrent in line 233 and'in local conductor 243, polarizing the grid ofvalve 282 to render its plate circuit non-conducting thereby startinggas-filled valve 231 into oscillation. Closing of contacts of relay 284places valve 340 under control of valve 263. During transmission ofsignals of intelligence, at all times one or the other of valves 231 and340will be oscillating and relay 269, having windings in both of the twoplate circuits, will beenergized continuously. I i 7 Circuit 23!,because it has an operating potential applied in series connection at amedian point between ground terminals 260 and 26!, manifests a positivepotential with reference to ground at resistor 262 in substation 230 andmanifests a negative potential with reference to ground at resistor 218in repeater station 232.

The marking condition of signaling in the substation 230 and in therepeating station 232 includes the oscillating condition of a gas-filledvalve 320 at substation 230 and 231 at repeating station 232. Atsubstation 230, a direct connection is made from line section conductor23! to grid of gas-filled valve 320 to render the valve conductive andoscillating, while at repeating station 232 the negative extensionconductor 211 is connected to grid of a signalreversing vacuum valve 263whose plate circuit is connected to grid of gas-filled valve 340. Thusat substation 230 a signal receiving oscillating valve is renderedactive in response to a positive condition of an associated signalingline circuit while at repeating station 232 a signal receivingoscillating valve is rendered active in response to a negative conditionof an associated signaling line circuit.

Structure of Fig. 3 comprises a conductor 46!! for received signals, aleak resistor 40! for discharging the conductor 400 to ground potentialupon cessation of a signaling current, a potential branch conductor 402to grid 403 of amplifying valve 404, a flashing lamp 405, a photo-cell406, resistor 461, a potential branch conductor 438 ductor 463 to grid445.

to grid 409 of amplifier valve 410, a battery 4! I, and an outputconductor 4 2.

In operation, a received marking signal of positive polarity uponconductor 420 will polarize the grid 403 to permit illumination of lamp405 to vary the potential impressed upon grid 409 to permit a signalcurrent of marking nature to flow in output conductor 4!2 from battery4!!. Interruption of signaling potential on conductor 400 will effectground potential upon grid 423, interrupting current from lamp 405 anddarkening the photo-cell 406, thus changing the potential supplied togrid 409 and interrupting the signaling current in output conductor 4!2.Received signals as ofv static electrical discharges, if too short ortoo Weak to illuminate the lamp 405, will not be repeated into conductor4!2.

, Structure of Fig. 4 resembles that of Fig. 3, but provides for a polaroutput suitable for doublecurrent working, comprising a conductor 42!]for received signals, a leak resistor 42! for discharging the conductor420 to ground potential after cessation of signaling current in lineconductor 420, a potential branch conductor 422 extending to grid 423 ofamplifying valve 424 which derives plate current from conductors 425,426 connected to ends of a high value resistor 42'! in a Wheatstonebridge structure 428 supplied with current from a battery 429 andsupplying current from detector-bridge points over conductors 430, 43!to a polar flashing lamp 432 serving two photo-cells 433, 434. Atwin-triode valve 440 has a common filament 44!, two independent plates442, 443 and two independent grids 444, 445 with circuits as follows: Aplate circuit for plate .442 including battery 450, filament 44!, plate442, conductor 45!, conductor 452, resistor 453, contactor 454, andconductor 455. A plate circuit for plate 443 including battery 456,filament 44!, plate 443, conductor 456, resistor 453, contactor 454, andconductor 455. A potentiometer circuit for grid 445 including battery460, conductor 46!, resistor 462, conductor 463, photocell 434, andconductor 464 and comprising further a potential branch conductor 465from con- A potentiometer circuit for grid 444 including battery 460,resistor 410, contactor 41!, resistor 412, conductor 413, photocell 433,and conductors 414, 46! and comprising further a potential branchconductor 415 which connects contactor 416 to grid 444.

In operation, a resting condition of a received signal of marking natureor positive potential on conductor 420 polarizes grid 423 positively andrenders the valve 424 conducting between conductor 425 and ground, thusrendering the shunted bridge arm 421 lower in resistance than itscompanion bridge arm 462. Current from battery 429 flows throughresistor 486 and valve 424 to ground without effect, flowing alsothrough resistors 48!, 482 to ground without effect and flowing throughresistor 48!, conductor 43!, lamp 432, conductors 430, and valve 424 toground, illuminating electrode 486 of lamp 432 controllingphoto-electronic cell 434, changing potential on grid 445 and offering apath for current from filament 44! to plate 443. Current flows fromnegative pole of battery 450 through cathode 44 anode 4'43 and conductor456 to ground, and from positive pole of battery 450 through conductor455, and contactor 454, thence through one part of resistor 453 andconductor 484 to ground without effect, and also flows effectivelythrough a remaining part of resistor 453, conductor 452 and outputconductor 485 with positive terminal oi battery 450 connected to outputconductor 485 and negative terminal of battery 45!! connected throughconductor 453 to ground, constituting a signaling condition of positivepotential or marking nature on output conductor 485.

A received signal of negative potential or spacing nature received onconductor 420 electrigrid 422 negatively, renders valve 424nonconducting and increases resistance from conductor 425 to ground.Current from battery 429 flows in the four resistors, 480, 421 to groundand 481, 432 to ground without efiect and flows also through resistor480, conductor 403, lamp 43-2, conductor 43! and resistor 432 to ground,illuminating electrode 483 of lamp 432, controlling photo-electroniccell 433, changing potential on grid 444 and ofiering a path for currentfrom filament 44I to plate 442. Current from battery 450 flows over anoutput circuit including ground, conductor 434, resistor 453, contactor454, conductor 455, grounded positive pole and free negative pole ofbattery 450, filament 44!, plate 442, and conductor 45l, whence currentflows through conductor 452 and resistor 453 Without effect, and alsofiows efiectively over output conductor 485, with negative terminal ofbattery 450 connected to output conductor 485 and positive terminalconnected through conductor 484 to ground, a signaling condition ofspacing nature on output conductor 485.

Thus as positive and negative telegraphic signals are received overconductor 420, each is amplified and retransmitted as a positive ornegative signal upon output conductor 485, except that received signalsas of static discharges which are too weak or too short to illuminatethe lamp 432 are not repeated.

The invention has been described by use of specific applications asexamples, but may be utilized in modified forms.

What is claimed is:

1. In a telegraph system, a normally continuously conducting signalingcircuit, a source of alternating potential in said circuit, athermoelectric space discharge rectifying tube having cathode and anodein said circuit, said circuit normally carrying a rectified current, athermoelectric triode tube having its cathode and anode in said circuit,means responsive to received signals for suppressing operation of saidsource to stop said current in signaling manner, and further meansresponsive to other received signals for polarizing the grid of saidtriode tube to stop said current in signaling manner.

2. In a telegraph two-way single line repeating system, two linesections, two normally nonoscillating thermo-electronic valves eachresponsive to a signal of commutated direct current received from one ofsaid line sections to begin oscillation and to generate a comparativelyrapid alternating current, rectifiers operated by said alternatingcurrent to supplyadirect-current signal to the other of said linesections, and further rectifying means associated with each of saidvalves and operative when said associated valve is oscillating togenerate alternating current and to rectify said alternating current toprevent oscillation of the other of said valves.

3. In a telegraph system, two line sections, two normally nonoscillating thermo electronic valves each having its grid connected toone of said line sections, means operative over one of said linesections to transmit a positive directcurrent signal to cause one ofsaid valves to oscillate, and means responsive to said valve inoscillation to generate a rapid alternating current and apply through arectifier a direct-current positive signal to the other of said linesections and to generate an alternating current and apply through arectifier to the grid of the other of said valves a direct-currentnegative potential.

4. In a telegraph system, two line sections, two thermo-electronicvalves each responsive to a positive signal upon its grid received fromone of said line sections to begin oscillation to generate a rapidalternating current and to apply through a rectifier a positive signalto the other of said line sections and to generate and apply to the gridof the other of said valves a negative potential, and a delaying filterbetween said rectifier and the line section to which said positivesignal is applied.

5. The method of repeating direct-current telegraph signals whichcomprises the steps of generating alternating currents in response toreceived direct-current signals, amplifying a portion of the alternatingcurrents, rectifying and retransmitting the rectified currents,amplifying a further portion of the alternating currents, and rectifyingand utilizing the further rectified currents to suppress reflectionsignals.

6. In a telegraph repeater, an amplifier valve directly responsive tomarking and spacing received signals of positive and negativepotentials, flashing lamps directly responsive to output signals fromsaid amplifier valve, photo-cells responsive to illumination by saidflashing lamps, and means controlled by the photo-cells for reproducingand retransmitting marking and spacing signals of positive and negativepotentials corresponding to the signals received by said amplifiervalve.

7. In a telegraph system, two telegraph stations, a transmission lineconnecting said stations and connected with ground return at eachstation, receiving tubes and potential branch conductors at eachstation, a source of current included in said transmission line inseries connection at a location between said potential branch conductorsof said line, line-signal responsive oscillatory means at one of saidstations controlled to oscillate in response to a receiveddirect-current signal of positive potential upon said line with respectto ground, and linesignal responsive oscillatory means at the other ofsaid stations controlled to oscillate in response to a receiveddirect-current signal of negative potential upon said line with respectto ground.

8. In a telegraph system, means for initiating oscillation comprising, arelay, an oscillatory system, a plurality of oscillators in said system,a control circuit including contacts of said relay for rendering saidsystem initially oscillatory when said relay is unenergized, and aplurality of energizing circuits for said relay rendering said relayresponsive to energization by a plurality of said oscillators.

9. In a telegraph system, two lines, means for impressing high-speeddirect current printer signals on either of said lines and a two-wayrepeater for relaying said signals from either line to the other line,said repeater comprising a source of oscillations of a relatively highfrequency compared to the frequency of said printer signals, two vacuumtubes having the input circuits thereto connected to the respectivelines, means including said vacuum tubes and source of oscillations forrepeating signals from each line to the other line and means responsiveto the transmission of signals over either line to the repeater forlocking out the other half of the repeater so long as the signalscontinue.

10. In a telegraph system, two lines and a twoway repeater adapted torepeat signals from either of said lines to the other line, saidrepeater comprising two space-discharge devices having their outputcircuit each associated with one of the respective lines, a source ofalternating current associated with each of said space-dischargedevices, means including said devices and said source for repeatingsignals received over either of the lines and means for preventing thesignal appearing in the output circuit of one of said space-dischargedevices from being repeated by the other space-dischargeldevice.

11. In a telegraph system, two lines, means for impressing signals onboth of said lines and a two-way repeater adapted to repeat said signalscheeses from either of said lines to the other line, said repeatercomprising a space discharge device, a source of alternating current anda rectifier for each line and means including either of saidspace-discharge devices and the associated rectifier for controlling oneof said lines in accordance with signals received over the other line.

12. In a, telegraph system, a line, means for impressing high-speeddirect current printer signals on said line, receiving means, meansconnected to said line and said receiving means for regenerating saidsignals, said last mentioned means comprising an oscillation generator,a space-discharge device connected to said line and arranged to controlthe connection of said generator to said receiving means and a rectifierbetween said generator and said receiving means.

LOUIS M. PO'I'IS.

